| January 2003. The Maldives sent photos of spots on banana fruits saying that they suspected fruit spot/eye spot/swamp spot caused by the fungus, Deightoniella torulosa (Syd.) M.B. Ellis. It was thought to be a minor disease, but recently it has become very serious on some islands.
There was a suggestion that it might be secondary to thrips as a similar condition occurred in the Yemen. It has been written up by S El Bashir & AH Al Zabidi (1985) Fruit Spotting of Banana in the Yemen Arab Republic. FAO Plant Protection Bulletin 33: 113-118. Until today banana farmers spray their crop heavily to kill thrips.
However, banana pathologists, thought that the disease is probably not all Deightoniella speckle as most
of the lesions are too big. Although some lesions appear to be protruding or flat, others appear sunken. It is hard to pinpoint the cause without a specimen and a history of the problem. There was a thought that the sunken lesions might be pitting disease caused by Pyricularia grisea. Isolations were needed.
Pitting disease gets its name from the round, sunken pits that appear on fruit as it approaches maturity. The pits ultimately average 4-6 mm in diameter and are surrounded by a reddish brown zone, which in turn is surrounded by a greenish, narrow, water-soaked halo. Although the pit centres sometimes split, the damage is confined to the peel and does not extend to the pulp. Under favourable conditions during transit and ripening, the number of pits may increase substantially. The pathogen does not sporulate on lesions on the fruit.
The fruit on the side of the bunch facing away from the pseudostem is more severely affected than fruit facing towards the pseudostem. The larger proximal hands have more lesions than the smaller distal hands. Small pits can also occur on the pedicels and crowns, which can cause finger drop. Symptoms are rarely seen in the field until 70 days after bunch emergence. The pathogen has been associated with rotting wood and is common in hanging banana leaf trash and bracts. Spores are more common in the air during periods of high rainfall.
Pitting disease is controlled by dithiocarbomates. Dusting under the polyethylene bunch cover, if they are used in the Maldives, has been shown to be effective.
Another possibility is brown spot, which is a disease that does not form sunken lesions on fruit. It is caused by Cercospora hayi, which is readily isolated from lesions. Symptoms occur on fingers, pedicels and crowns. Spots are pale to dark brown with an irregular margin, surrounded by a halo of water-soaked tissue. The size of the spots, which are centred on stomata, varies, but they average 5-6 mm in diameter when mature. These spots do not increase in size and number during ripening as do pitting disease spots. Brown spot occurs on fruit that is 50 days old or older. The pathogen does not sporulate in spots. It is controlled in the same way as pitting disease.
If the problem does not seem to be either of the above, what about a reaction to a herbicide or some other chemical? Could sucking insects be involved? Are some cultivars affected more than others? What cultivar is the fruit in the pictures? |
